Studies on Regulation. 547 



greater than elsewhere; hence the "abnormal" or as it might be 

 called "regulative" distribution of these branches. 



But the absence of intestinal branches in the pharyngeal region 

 in these pieces is itself a fact of importance. Though I was un- 

 able to determine w^ith certainty the particular conditions to which 

 this absence of regeneration is due certain points which appeared 

 to me suggestive may be mentioned here. First of all it must be 

 remembered that in the absence of food the intestinal contents 

 decrease in amount during the course of these experiments and 

 consequently internal pressure diminishes; the movements and 

 muscular contractions force the contents into one part or another 

 of the intestine thus producing distension now in one region, now 

 in another; secondly, the regions of greatest muscular activity are 

 the regions anterior and posterior to the pharynx, especially the 

 former; and it is in these regions that the movements of the intes- 

 tinal fluid are visibly most frequent and powerful. The lateral 

 margin of the body in the middle region shows much less motor 

 activity than the terminal regions and in pieces in which the longi- 

 tudinal axis is bent by contraction of one side this difference is 

 especially marked on the concave side. And finally, when con- 

 traction of the longitudinal muscles occurs and the intestinal 

 contents are forced back toward the pharyngeal region the concave 

 side of the body becomes still more concave and the new tissue of 

 thi^ side is pressed together and often thrown into folds, a con- 

 dition which must retard or prevent the growth of intestinal 

 branches into this region. In short, I am inclined to believe that 

 the form of the piece and the distribution by means of muscular 

 activity of internal pressure due to intestinal contents are the 

 chief factors in preventing regeneration of the intestinal branches 

 in the pharyngeal region. 



In all cases where the plane of section is far to one side of the 

 median plane the amount of regeneration is even less than in the 

 left piece of Series 64. Moreover, as the distance between the 

 median plane and the plane of section increases the rapidity and 

 amount of regeneration decreases and the life of the pieces be- 

 comes shorter; narrow strips from the lateral regions of the body 

 living only a few days and showing scarcely any regeneration. 



